End face seals are commonly used in severe service environments to exclude external contaminants such as grit, water, and the like from joints between relatively movable members and to retain lubricants therein. One such application for seals of this type is in the pin joints in endless track chains on track-type earthmoving vehicles. Such track chains operate in extremely abrasive environments, and the track joints may be exposed to mud, dust, sand or rock at temperatures which may reach the extremes found in either the deserts or the artic regions. Such seals perform their primary sealing function under these conditions, because the sealing portions thereof are precisely formed to mate with and sealingly engage the end faces of their associated bushings and because the annular seal rings themselves are accurately positioned and maintained under a substantial axial face load by an elastomeric load ring.
In order to function successfully under these relatively severe conditions, the seal must not only possess strength, corrosion resistance, and abrasion resistance, but also must be able to withstand the shock associated with earthmoving operations, even when carried out at subzero temperatures. In addition, it is desirable to have a seal possessing a combination of the properties of sealability, seal face stability, a low coefficient of friction and stiffness to resist deformation of the seal face or sealing lip under load. Accordingly, track seals are frequently constructed from two different materials; the sealing lip portion being formed from a relatively pliable material such as polyurethane rubber. The sealing tip is then bonded to a relatively stiff support ring formed from a polycarbonate plastic material, one type of which is available commercially under the trade name Lexan.
While end face seal assemblies having two-piece annular seal rings have demonstrated improved performance over seal assemblies of earlier designs, the requirement for a functional bond exposed to the hostile environment on one side and the lubricant on the other is an inherent weakness in the assembly. Failure of the rubber/polycarbonate bond may cause seal leakage and ultimate track joint failure. Considering the fact that there are approximately two hundred such seals on a tractor, one appreciates that a seal ring failure rate of one tenth of 1.0%, i.e. one out of every one thousand may result in premature track pin joint failure and expensive and highly undesirable downtime for one out of every five vehicles.
The foregoing illustrates limitations of the known prior art. In view of the above, it would be advantageous to provide an alternative to the prior art.